speex: fix CVE-2020-23903

Backport patch to fix CVE-2020-23903.

CVE: CVE-2020-23903

Signed-off-by: Kai Kang <kai.kang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit b8f56e5e)
Signed-off-by: Steve Sakoman <steve@sakoman.com>